Large composite structures may be fabricated using automated equipment such as automatic tape laying machines and automatic fiber placement machines. These automated machines layup plies over a tool by laying down multiple courses of prepreg tape or tows. Automated layup of prepregs has several disadvantages, including the relatively short shelf-life of the prepreg materials, potential gumming of tape placement heads, the need for capital intensive autoclaves for curing and limitations in the variety of prepreg formats that are available.
Some of the disadvantages mentioned above may be overcome using liquid molding techniques such as, without limitation, resin infusion of fiber preforms. However, the resin infusion process also has certain disadvantages, including limited flexibility in controlling the location and deposition of resin into conventional tooling and difficulties in infusing high modulus and highly toughened resins into large structures. Also, resin infusion is time consuming and requires relatively complex bagging arrangements and resin transfer systems and may require technicians to come into direct contact with resins. Furthermore, resin infusion may be relatively costly in terms of material waste and consumables.
In order to improve resin distribution and reduce processing times, it has been proposed to infuse fiber preforms using pieces of resin film that are sectioned from a large sheet and placed on a mandrel followed by a dry preform. A relatively complex dam and various consumables are required in order to control resin flow. Accordingly, the resin film infusion process and equipment may not be well suited to higher production environments where automation is desirable.
Resin spray techniques have been employed in which resin is deposited using a spray gun by automated means onto a tool. However this process requires that the tool be maintained at low temperatures in order to control the change of state in the resin from a liquid to a solid when transferred from the spray gun to the tool.
Accordingly, there is a need for a method of fabricating composite structures, particularly large scale structures, using a resin infusion process that reduces costs and is well suited to automation. There is also a need for a method and apparatus for automated deposition of resin films that allow high laydown rates, improved control over resin quality, location and distribution and which permits the use of high modulus and toughened resins.